Omnidirectional antenna



June 5, 1956 s I 2749,5 14

OMNIDIRECTIONAL ANTENNA Filed May 29, I953 INI'EVIUR. i ALFRED S. PIKEUnited States Patent OMNIDIRECTIONAL ANTENNA Alfred S. Pike, Rochester,N. Y., assignor, by mesnc assignments, to General Dynamics Corporation,a corporation of Delaware Application May 29, 1953, Serial No. 358,311

2 Claims. (Cl. 343-742) My invention relates to horizontally polarizedomnidirectional antennas and more particularly to omnidirectionalantennas of the square loop type.

My invention is particularly applicable to the square loop type ofomnidirectional antenna which comprises a pair of Z-shaped elementssuperimposed in a square configuration, with the corresponding ends ofthe elements adjacent each other at diagonal corners of the square. Thefeed point is at the center of each of these elements. Theconfiguration, usually referred to as an Alford antenna, is shown inFig. 1. The sides of the square are preferably a quarter of a wavelength long at the center of the band of frequencies over which theantenna is to be operated. This type of antenna is described, forexample, in J. D. Kraus, Antennas, McGraw-Hill Book Company, New York,1950, at page 429.

Those who have used this type of antenna at very-high and ultra-highfrequencies have found that the current distnibution around the loop isnot uniformly strong. The current distribution produces a pattern whichis generally oval in configuration rather than circular, as is desiredin omnidirectional antennas.

It is accordingly an object of my invention to provide a new andimproved horizontally-polarized omnidirectional antenna.

It is another object of my invention to provide a horizontally-polan'zedomnidirectional antenna having a closer approach to circularity atvery-high and ultra-high frequencies than the square-loop type ofantenna just described.

Further objects and advantages of my invention will become apparent asthe following description proceeds and the features of novelty whichcharacterize my invention will be pointed out with particularity in theclaims annexed to and forming a part of this specification.

For a better understanding of my invention, reference may be had to theaccompanying drawing in which:

Fig. 1 shows the schematic configuration in plan view of the square-looptype of antenna under discussion;

Fig. 2 shows a second such antenna configuration in plan view;

Fig. 3 is an edge view of an antenna according to my invention; and

Fig. 4 is a plan view of the embodiment of my invention shown in Fig. 3.

The loop antenna shown in Fig. 1 comprises a pair 1 and 2 of Z-shapedelements superimposed in a square configuration. Corresponding ends 3and 4 of the two elements are placed adjacent each other on one cornerof the loop configuration while the other corresponding ends 5 and 6 areplaced adjacent each other at the diagonally-opposite corner of thesquare. Element 1 is fed at its center point 7, while element 2 is fedat its center point 8.

The loop configuration indicated in Fig. 1, while generally thought tohave a current distribution substantially uniform around the square, inactuality has the current distribution shown by the dashed lines. Inaccordance with my invention, I provide a pair of loops of the typeshown in Fig. l. I orient the first of these loops as shown in Fig. 1,for example, and the second as shown in Fig. 2. The loop shown in Fig. 2is substantially identical with that shown in Fig. 1, except that theantenna in Fig. 2 is rotated substantially in the horizontal plane withrespect to the first loop. The current distribution of the loop shown inFig. 2 is substantially the same as that shown in Fig. 1, except, ofcourse, it is rotated by 90 in the horizontal plane because of theorientation of the loop.

In accordance with my invention, the loops oriented as shown in Figs. 1and 2 are positioned one above the other in the fashion shown in Fig. 3.I prefer that the vertical separation between the two square loops be anegligible fraction of the wave length at which the loops resonate. Forexample, if the loops resonate at mc./s., a vertical separation on theorder of $6" is satisfactory.

The loop of Fig. l is conventionally fed at points 7 and 8 and that ofFig. 2 at points 9 and 10. Further in accordance with my invention, Iparallel points 7 and 9 and likewise points 8 and 10 to provide aparallel feed for the two loops. The parallelled feedpoints are chosento provide additive currents in the two loops, rather than subtractive.The feed points may be connected, via line 11, 12, to a conventionalsource of energy or to a receiver as the need may be; such units are notshown, for they form no part of my invention. The individual currentdistribution patterns of the loops of Fig. 1 and Fig. 2 combine when inthe position of Fig. 3 to provide the substantially improveddistribution pattern shown by dashed lines in Fig. 4. Thus, the primaryobject of my invention is shown to have been achieved.

While I have shown and described my invention as applied to a specificembodiment thereof, other modifications will readily occur to thoseskilled in the art. I do not, therefore, desire my invention to belimited to the specific arrangement shown and described, and I intend inthe appended claims to cover all modifications within the spirit andscope of my invention.

What I claim is:

1. In a substantially horizontally polarized omnidirectional antenna,the combination of a pair of square loop antennas of the type comprisinga pair of substantially Z-shaped elements superimposed in a squareconfiguration, with the corresponding ends of said elements adjacenteach other at diagonal corners of said square configuration and with acenter feed point for each said element, one of said square loops beingplaced directly above the other and oriented substantially at a 90 anglein the horizontal plane with respect to the other of said loops, saidloops being fed in parallel at said center feed points of said elements.

2. The combination of claim 1 in which said loops are verticallydisplaced by a distance which is a negligible fraction of the wavelength at which said loops resonate.

References Cited in the file of this patent UNITED STATES PATENTS AlfordMay 26, 1942 OTHER REFERENCES

